Long Term Evolution (LTE)
Third-generation mobile systems (3G) based on WCDMA radio-access technology are being deployed on a broad scale all around the world. A first step in enhancing or evolving this technology entails introducing High-Speed Downlink Packet Access (HSDPA) and an enhanced uplink, also referred to as High Speed Uplink Packet Access (HSUPA), giving a radio-access technology that is highly competitive.
However, knowing that user and operator requirements and expectations will continue to evolve, the 3GPP has begun considering the next major step or evolution of the 3G standard to ensure the long-term competitiveness of 3G. The 3GPP launched a Study Item “Evolved UTRA and UTRAN” (E-UTRA and E-UTRAN). The study will investigate means of achieving major leaps in performance in order to improve service provisioning and reduce user and operator costs.
It is generally assumed that there will be a convergence toward the use of Internet Protocols (IP), and all future services will be carried on top of IP. Therefore, the focus of the evolution is on enhancements to the packet-switched (PS) domain.
The main objectives of the evolution are to further improve service provisioning and reduce user and operator costs as already mentioned.
More specifically, some key performance and capability targets for the long-term evolution are:                Significantly higher data rates compared to HSDPA and HSUPA: envisioned target peak data rates of more than 100 Mbps over the downlink and 50 Mbps over the uplink;        Improved coverage: high data rates with wide-area coverage;        Significantly reduced latency in the user plane in the interest of improving the performance of higher layer protocols (for example, TCP) as well as reducing the delay associated with control plane procedures (for instance, session setup);        Greater system capacity: threefold capacity compared to current standards.        
Another key requirement of the long-term evolution is to allow for a smooth migration to these technologies.
Mobility Management
For mobility management in a system with heterogeneous access networks different protocols may be applied. On the one hand global mobility protocols may be used for inter Access System mobility. A well-known example for a global mobility protocol is the client-based network layer protocol Mobile IP (MIPv6). With this protocol the mobility is transparent on a mobile node for layers above the network layer. On the other hand local mobility protocols are used for intra Access System mobility, examples thereof are NetLMM or GTP. Especially these two examples are network-based, i.e., their use is completely transparent to the mobile node, in particular the network layer. NetLMM is IP-based and independent of the underlying network technology, whereas GTP is especially for the 3GPP network and is coupled with the technology, e.g., relies on 3GPP specific identifiers.
MIPv6
Using Mobile IPv6 as specified in RFC 3775 (available at http://www.ietf.org, incorporated herein by reference) a mobile node (MN) is reachable by its home address even when away from home. For this the mobile node is associated with a care-of address (CoA), which provides information about the mobile node's current location. The home agent (HA) of the mobile node and also a correspondent node (CN) set up a binding between the home address and the care-of address in a cache and packets destined for the mobile node are directly sent to the care-of address. If the mobile node is at its home network, it deregisters the care-of address and receives packets directly with its home address.
In order to allow a home agent to intercept traffic for a node the proxy Neighbor Advertisements of the Neighbor Discovery protocol are used. According to Mobile IPv6 if there is a binding cache entry in the home agent for a mobile node, the home agent sends proxy neighbor advertisements so that the neighbor cache entries of the nodes in the vicinity of the home agent are updated and all traffic to the mobile node is sent to the link-layer address of the home agent.
In the IETF (Internet Engineering Task Force) discussions are ongoing how to enhance Mobile IPv6 to support Mobile Nodes with multiple interfaces. This simultaneous use of the multiple interfaces increases service quality for the terminals and makes better use of the network capacity.
Mobile Node Returning “Home”
When returning home, i.e., one of the mobile node's interfaces is attached to the home link, two possible approaches are described in the state of the art.
In the first approach the mobile node sends a binding update to the home agent with its home address as a care-of address, the home registration bit set and lifetime set to zero, to instruct its home agent to no longer intercept or tunnel packets for it. In this case the home agent deletes the binding of the mobile node from the binding cache and stops sending proxy neighbor advertisements in behalf of the mobile node. On the other hand the mobile node starts to send neighbor advertisements with its own link-layer address on the home link, so that the neighbor cache entries in the routers are changed and all traffic is directly sent to the mobile node.
In a second approach the mobile node de-registers the binding for the interface on the home link and stops using the interface. In this case all traffic previously sent to the de-registered interface is then sent to the remaining registered interface, i.e., through a foreign network to which the mobile node is still connected.
In both scenarios it is not possible for the MN to use the home link and a foreign link simultaneously.